Electromagnetic receiving and transmitting instrument



A. A. THOMAS Sept. 13, 1932.

ELECTROMAGNETIC RECEIVING AND TRANSMITTING INSTRUMENT Filed Oct. ll, 1927 aluc'nl'o'z Patented Sept. 13, 1932 UNITED STATES ADOLPH A. THOMAS, F NEW YORK, N. Y.

ELECTBOMAGNETIC RECEIVING AND TBANSMITTING INSTRUMENT Application led October 11, 1927. Serial No. 225,586.

This invention is for an electromagnetic receiving and transmitting instrument of novel construction and highly efficient operation. My new device possesses special advantage as a loudspeaker unit, but the invention 1s not restricted to that particular field.

In a preferred embodiment ofmy invention I employ a vibratory armature unit consisting of a pair of magnetic spring blades or tongues mounted at one end on a pole plece of the field magnet frame. The other ends of the armature blades are connected together and extend on opposite sides of the other magnet pole piece but out of contact f therewith, whereby the armatures provide two parallel magnetic paths between the pole pieces with an airgap in each path. In the normal position of the armatures, the alrgaps are substantially equal, so that the normal field flux divides about evenly through the armatures and thus holds them magnetically balanced. The armatures are connected at or near their free ends to a suitable vibratory member, which may be an acoustic dia- 'r phragm, a recording tool, a' reproducing stylus, or any other element capable of performing a desired function. One or both of the armatures are surrounded by a coil or coils which produce unlike polarities of variable intensities at the free ends of the armatures when the instrument is used as a receiver. The result is vibration of the armature tongues as a unit without lost motion to actuate the connected member. When the V device is used as a transmitter, vibratory movement of the armature unit generates electric impulses in the coil 'or coils.

The magnet field in my new instrument is preferably furnished by a permanent mag net having a closed body rovided with a pair of pole pieces substantia ly midway thereof.

This construction gives two parallel paths for the flux between the ole pieces, which are thus in the center of a alanced magnetic system. Perhaps the best form of magnet to use is a flat circular magnet with diametric pole pieces, since such a magnet can easily be stamped or punched out of sheet steel, either solid or laminated. The novel features and practical advantages of my invention will be clear from a detailed description of the accompanying drawin in whichig. l shows a driving unit constructed in accordance with my invention, this view being a section on line 1-1 of Fig. 2;

Fig. 2 represents a section on line 2-2 of Fig. 1;

Fig. 3 is a section on line 3 3 of Fig. 2; and

Figs. 4 and 5 are diagrams illustrating the operation of the instrument.

The parts comprising the instrument are housed in a casing 10, which is here shown of cylindrical shape having an integral back 12 and removable front plate 13.

This casing may be made of non-magnetic metal, such as aluminum, brass, or the like, or it may be molded out of a suitable composition, such as bakelite, for instance. The cover plate 13 is removably secured to the body of the casing by screws 14 which enter enlargements or projections 15 formed integral with the cylindrical body of the casing. The back plate 12 of casing 10 is provided with posts or studs 16 on which a magnet M is supported. These posts or studs may be formed integral with plate 12. Screws 17 engaging the studs 16 hold the magnet M rigidly mounted in proper position within the casing. As seen in Figs. 2 and 3, the magnet is spaced about midway between the front and back of the casing. To facilitate the correct insertion of the magnet into the casing, the circular body of the magnet is formed with recesses 18 adapted to receive the projections 15 when the magnet is positioned in proper relation to the mounting posts 16.

The field magnet M may be an electromagnet, but I prefer to make it of the permanent type. It can he stamped or punched out of sheet steel, either solid or laminated. From the circular body of the magnet project two integral arms 19 and 20, which extend toward each other along a diametric line and constitute the pole pieces of the magnet. It is not absolutely necessary that the magnet M shall be circular, for it may have any other closed shape with inwardly extending pole pieces. One practical advantage of making the magnet circular is that a maximum length of magnetic path may be housed in a space of minimum diameter.

To one of the magnet pole pieces (in this instance the pole piece 19), is secured a vibratory armature unit comprising a pairof resilient blades or tongues 21 and 22, which may conveniently be cut from long bars or strips of magnetic spring metal having the required degree of elasticity. Suitable fastening devices 23', such as bolts, rivets or the like, secure one end of the armature tongues to opposite sides of pole piece 19, while the free ends of these tongues extend on opposite sides of ole piece 20, but out of contact therewith. s seen in Fig. 2, this construction provides a pair of parallel magnetic paths between the pole pieces 19 and 20, with an airgap 23 and 24, respectively, in each path. The armature blades or tongues 21 and 22 are rigidly connected near their free ends by a rod 25 and a bushing 26. The rod 25 is firmly attached to the armature blade 22 and is in screw-threaded engagement with bushing 26, which is rotatably mounted on armature blade 21. The bushing 26 terminates in a screwead 27, by means of which the bushing is adjustable to vary the distance between the armature blades 21 and 22. A hole 27 in cover plate 13 permits the insertion of a screwdriver to adjust the bushing. The normal set of the spring members 21 and 22 is such that they tend to spring apart at their free ends. Consequently, when these members are connected by the parts 25 and 26, they are held under constant tension, thereby taking up any looseness or play due to the adjustable bushing 26. In other words, the armature members 21 and 22 always vibrate as a unit without lost motion. If necessary or desirable, these tongues or blades may be thinned at the pivot points 21 and 22 to increase their elasticity. Except at the points where they bend during vibration, the armature tongues are substantially rigid and fully capable of handling the load imposed upon them by the member connected to rod 25.

A pair of coils 28 and 29 surround the armature tongues 21 and 22, respectively, and are held in position by non-magnetic brackets 30. These brackets may conveniently be mounted on the body of magnet M, as by screws or other fastening means 31, whereby the magnet and all the parts carried thereby can be inserted as a unit into the casing. The axial openings 32 of coils 28 and 29 allow free movement of the armature members at maximum amplitude. As shown in Fig. 2, the coils 28 and 29 may rest on top of pole piece 19, and the oppositely arranged brackets 30 hold the coils centered with respect to the armature tongues. The brackets 30 are preferably made of spring metal, so that they exert a eentralizing pressure against the coils at opposite sides.

The operation of the instrument above described as a receiver or driving unit for acoustic diapliragms will bel readily understood from the diagrams of Figs. 4 and 5. The coils 28 and 29 are so connected that at any instant they induce. opposite polarities in the free ends of the resilient armature tongues 21 and 22. In Fig. f1, the indicated polarities of the field magnet and the armature unit show that the free end of the armature 21 is attracted to pole piece 20, while the free end of armature 22 is at the same time repelled from that pole piece. Consequently,

the armature unit moves toward the right, as indicated by arrow a. lVhen the electric impulses passing through' the coil or coils 28 and 29 induce the armature polarities indicated in Fig. 5, the armature 22 is attracted to pole piece 20, while the armature 21 is simultaneously repelled from that pole piece. The armature unit moves therefore toward the left, as indicated by arrow b. This simultaneous attraction and repulsion of the armature members 21 and 22 produces great driving power, which is communicated without lost motion to the connection 25. Since the driving rod 25 is connected to the armature unit between the fixed and vibratory ends thereof, the vibratory armature exerts an increased leverage on the rod. This is of special advantage in operating large cone diaphragms, which require small movement but considerable driving power. It will be understood that the resilient armature members 21 and 22 have sufficient cross-sectional area to transmit the field flux without saturation, so that variable current impulses in coils 28 and 29 instantly produce corresponding variations in the magnetic flux passing through the armature unit.

When the instrument is used as a receiver, the mechanical vibrations of the armature members 21 and 22 produce 'ux variations therein, so that corresponding current impulses are generated in the coil or coils 28 and 29, which are so connected in circuit as to operate suitable receiving apparatus. This will be understood without further explanation.

My new electromagnetic instrument is also adapted to operate a phonograph recording tool by connecting the rod 25 to a suitable cutting or engraving stylus. It will also be apparent that, by attaching a reproducing stylus to the vibratory armature unit 21--22, the instrument will operate as an electric pickup. Since the vibratory armature 21--22 operates without lost motion, my device is particularly adapted for phonographie recording and reproducing.

The resilient armature tongues or blades 21 and 22 are normally in such position that the airgaps 23 and 24. are substantially equal, so that the armature unit is magnetically balanced. This means that normally there is no push or pull on the member connected to the driving rod 25. By turning the bushing 26, thev normal width of the airgaps 23 and 24 is regulated to give the best results in any given case. The normal width of the airgaps 23 and 24 and the inherent resiliency of the armature tongues are such that the free ends of the latter do not strike the pole piece even at maximum vibration. The airgaps 23 and 24 need be but a very small fraction of an inch. If necessary, elastic pads of rubber or other non-magnetic material may be inserted in the air gaps in yieldable pressure contact with the armature s ring blades and pole piece 20 to dampen un ue movement of these blades at their natural period of vibration, without otherwise interfering with the operation ofthe armature unit. When in the description and claims I refer to the armature parts 21 and 22 as spring blades or resilient lades, I use the expression broadly to include any practical form of vibratory rod, bar, arm, lever and the like.

It will be clear from the foregoing explanation that I have provided an electromagnetic receiver and transmitter of simple construction, in which the parts are few and rugged, and are easily made and quickly assembled. The actual device can be made considerably smaller and more compact than the device as illustrated, since I have purposely exaggerated the proportions and dimensions of the parts in order to make the drawing easy to read. It will therefore be understood that the drawing is not to be regarded as mathematically accurate shop drawing.

Although I have shown and described a specific construction, I want it understood that my invention is not limited to the details set forth. It is possible that changes and modifications will occur to those skilled in the art without departing from the scope of the invention as defined in the following claims.

I claim as my invention:

l. In an electromagnetic device, a magnet having two pole pieces, a pair of resilient armatures secured at one end to opposite sides of one of said pole pieces, the free ends of said armatures extending on opposite sides of the other pole piece but out of contact therewith, whereby said armatures provide two parallel magnetic paths between said pole pieces with an airgap in each path, a coil surrounding at least one of said ar1natures, and means for connecting the free nds of said armatures to a vibratory mem- 2. In an electromagnetic device a magnet frame consisting of a closed body having a pair of pole pieces extending toward each other substantially midway of said body, a pair of resilient armatures secured at one end to opposite sides of one of said pole pieces, the free ends of said armatures extending on opposite sides of the other pole piece but out of contact therewith, whereby said armatures provide two parallel magnetic paths between saidpole pieces with an airgap in each path, a coil surrounding each armature, means for mounting said coils on said magnet frame, and means for connecting the free ends of said armatures to a. vibratory member.

3. An electromagnetic device comprising a cylindrical casing, a Hat magnet frame consisting of a closed ring-shaped body having a pair of diametric pole pieces extending toward each other in a plane substantially parallel with the plane of said body, means in said casing for securing said magnet frame therein and holding it spaced from the front and rear walls of the casing substantially parallel therewith, cooperating means on said casing and said magnet frame to insure the correct positioning of said frame in said easing, said positioning means being independent of said securing means, and electromagnetic means operatively associated with said magnet frame.

4. In an electromagnetic device having a magnet provided with a pair of pole pieces, a vibratory armature unit operatively mounted on said magnet, said unit consisting of a pair of resilient blades secured at one end to opposite sides of a pole piece, the free ends of said blades extending on opposite sides of the other pole piece but out of contact therewith, and means for rigidly but non-magnetically connecting the free yends of said armature blades, so that the latter vibrate as a unit.

5. In an electromagnetic device, a magnet having two pole pieces, a pair of resilient armatures secured at one end to opposite sides of one of said pole pieces, the free ends of said armatures extending on opposite sides of the other pole piece but out of contact therewith whereby sai-d armatures provide two parallel magnetic paths between said pole pieces with an airgap in each path, a coil surrounding at least one of said armatures, means for connecting the free ends of said armatures to a vibratory member, and means for adjusting the distance between the free ends of said armatures to regulate the normal width of said airgaps.

6. In an electromagnetic device, a cylindrical casing provided with a projection, a circular magnet having a recess adapted to receive said projection to permit insertion of the magnet into the casing, means for securing the inserted magnet in said casing, and electromagnetic operating means mounted on said magnet, so that said magnet and said means are insertable into and removable from the casing as a unit.

7. In an electromagnetic device having a magnet provided with a pair of pole pieces, a vibratory armature unit operatively mounted on said magnet, said unit consisting of a pair of resilient blades secured at Vone end to opposite sides of a' pole piece,pthe

free ends of said blades extending on opposite sides of the other pole piece but out of contact therewith, and means for connecting said blades under tension at a point between said pole pieces.

8. In an electromagnetic device, a magnet having a pair of pole pieces extending toward each other and separated by a ixed airgap, a resilient armature blade secured'iiatwise at one end to one of said pole pieces, the free end of said blade extending past the other pole piece in close proximity thereto so as to provide a variable airgap outside of said fixed airgap, a coil surrounding said armature blade, and a connection secured to said blade at a point between said pole pieces, said connection extending substantially lat right angles to said blade.

9. In an electromagnetic device, a magnet having a pair of pole pieces, a pair of resilient armature blades securedlatwise at one end to opposite sides of one of said pole pieces, the Jii'ee ends of saidg-.blades extending on opposite sides of the other pole'piece but spaced therefrom to provide two airgraps, a coil surrounding each armature blade, and a connection secured to said blades at a point between said pole pieces.

10. Electromagnetic mechanism comprising a magnet having a closed body provided with a pair of pole pieces extending toward each other substantially midway thereof, a resilient armature secured at one end to one of said pole pieces and extending at its free end toward the other pole piece, a coil in operative relation to said armature and means for connecting said armature -to a vibratory member, said connecting means projecting through .the space between said pole pieces substantially at right angles to the plane of said magnet.

11. In an electromagnetic device, the combination of a field magnet structure, a vibratory armature unit consisting of a pair oi spring blades supported at one end on said structure in substantially parallel spaced relation and rigidly connected together near their other ends.

12. In an electromagnetic device, the combination of a magnet and a vibratory armature unit consisting of a'pair of resilient blades mounted at one end on a pole of said magnet in substantially parallel spaced relation and connected together near their other ends by non-magnetic means, and means for adjusting said connecting means.

13. In an electromagnetic device, a vibratory armature unit consisting of a pair of spring blades flexibly supported at one end and held spaced under tension at their other ends which are magnetically separated, and means for holding 'said other ends of the spring blades in fixed spaced relation.

14. In an electromagnetic device, a vibratory armature unit consisting-of a pair of spring blades mounted at one end in substantially parallel spaced. relation and con-A nected together under tension near their other tends, and means for adjusting said connecting means.

15. In an electromagnetic device having a magnet provided with a pair of pole pieces, a vibratory armature mounted on said magnet, said unit consisting of a pair of resilient blades secured at one end to opposite sides of a pole piece, the free ends of said blades extending on opposite sides of the other pole piece but out of contact therewith to provide two airgaps, and an adjustable connection between the free ends of said armature blades for varying said airgaps. y

16. In an electromagnetic device, a ma et having a pair of pole pieces, a pair o resilient armature blades secured flatwise at one end to opposite sides of one of said pole pieces, the free ends of said blades extending on opposite sides of the other pole piece but spaced therefrom to provide two airgaps, a connection secured to said blades at a point between said pole pieces, means for adjusting said connection to vary said airgaps, and one or more coils in operative relation to said armature blades.

17 In an electromagnetic device having a magnet provided with a pair of pole pieces, a vibratory armature unit operatively mounted on said magnet, said unit consisting of a pair of magnetic spring blades Secured at one end to opposite sides of a pole piece, the free ends of said blades extending on opposite sides of the other pole piece but out of contact therewith, and means for connecting said blades under tension at a point between said pole pieces, saidconnecting means including la rotary member for adjusting the distance between saidH blades.

18. An electromagnetic device comprising a cylindrical casing, a flat magnet frame consisting of a closed circular body having a pair of diametric pole pieces extending toward each other, means in said casing for securing said magnet frame therein and holding it spaced from the front and rear walls of the casing substantially parallel therewith, a vibratory armature secured at one end to one of said pole pieces, the other end of said armature extending in close proximity to the other pole piece but out of contact therewith to provide an airgap, a coil surrounding said armature, and a connection near the free end of said armature.

19. In an electromagnetic device, a magnet frame consisting of a closed body having a pair of pole pieces extending toward each other substantially midway of said body, a pair of resilient armatures secured at one end to opposite sides of one of said pole pieces, the free ends of said armatures exunit operatively tending on opposite piece but out of contact therewith, whereby said armatures provide two parallel'magnetic paths between said pole pieces'wlth an airgap in each path, a coil surrounding each armature, oppositcly arranged brackets car ried by said frame to hold said coils firmly in position, and means -for connecting the free ends of said armatures to a vibratory member. l

20. Electromagnetic mechanism comprising a cylindrical casing, a flat magnet frame consisting of a closed circular body having a pair of diametric pole pieces extending toward each other, studs in said casing for securing said magnet frame therein and holding it spaced from the front and rear walls of the casing substantially parallel therewith, a pair of resilient armatures secured at one end to opposite sides of one of said pole pieces, the free ends of said armatures extending on opposite sides of the other pole piece but out of contact therewith, whereby said armatures provide two parallel magnetic paths between said pole pieces with an airgap in each path, a pair of coils mounted on said magnet frame and surrounding said armatures, and means for connecting the free ends of said armatures to a vibratory member.

21. In an electromagnetic device, the combination of a magnet having two poles, and a vibratory armature unit comprising a pair of resilient arms connected at one end to a magnet pole and extending at their free ends on opposite sides of the other magnet pole but out of contact therewith, and means whereby said arms always vibrate in the same direction. v

22. In an electromagnetic device, the combination of a field magnet structure, a vibratory armature unit consisting of a pair of bars connected at one end to said magnetic structure in substantially parallel spaced relation, and non-magnetic means for rigidly connecting said bars near their free ends.

23. In an electromagnetic device having a magnet, an armature operatively associated with said magnet and consisting of two spaced reeds supported at one end on said magnet, the free ends of said reeds being separated from a magnet pole by two airgaps, and means for simultaneously producing opposite polarities at the free ends of said reeds.

24. In an electromagnetic device having a magnet provided with a pair of pole pieces, a vibratory armature unit consisting of a pair of reeds secured at one end to opposite sides of a pole piece, the free ends of said reeds extending toward the other magnet pole and separated therefrom by two airgaps, and means for polarizing said reeds.

25. In an electromagnetic device having a magnet, an armature consisting of two spaced reeds connected at one end to a magnet pole and extending toward the other pole from sides of the other polel which the 'free ends of said reeds are separated by two airgaps, a speech coi]L surrounding each reed to polarize the same in such a way that the field magnet exerts a push-pull eect on said reeds, and a vibratory member connected to said armature.

26. Electromagnetic mechanism comprising a magnet having a closed body provide with a pair of pole pieces extending toward each other substantially midway thereof, a resilient armature secured at one end to one of said pole pieces 'and extending at its free end toward the other pole piece, a coil in op'- erative relation to said armature, and means for connecting said armature to a vibratory member, said connecting means projecting substantially at right angles to the plane of said magnet.

27. In an electromagnetic device, a magnet having a pair of pole pieces separated by a xed airgap, a spring armature secured at one end to one of said pole pieces and extending toward the other pole piece to form therewith a variable airgap outside of said fixed airgap, a vibratory member, a connection between said armature and member, said connection extending through said fixed airgap, and a coil in operative relation to said magnet and armature.

28. In an electromagnetic driving mechanism for loudspeakers, the combination of a permanent field magnet system having pole pieces, a pair of vibratory armature bars resiliently mounted on said magnet system in substantially parallel spaced relation and rigidly connected to operate as a unit, said armature bars being so arranged that the field flux normally exerts substantially equal and opposite effects on said bars which are thus magnetically balanced, and a pair of speech coils arranged to upset said magnetic balance by increasing the resultant magnetic effect on one armature bar and simultaneously decreasing said effect on the other bar, whereby the two armature bars vibrate.

29. In electromagnetic driving mechanism for loudspeakers, the combination of a permanent field magnet system, a pair of spaced armature bars connected to vibrate as a unit, said armature bars being so arranged that the field flux passes therethrough in parallel paths, means for supporting said armature v bars wholly on said magnet system, and a stationary coil supported independently of said armature bars to vary the magnetic effect of said magnet system on said armature bars, said coil being so arranged that current impulses flowing therein cause the field flux in one of said paths to increase over the flux in the other path, whereby said armature bars vibrate with respect to said field magnet system.

30. In an electromagnetic device, a vibratory armature structure comprising two magnetic spring arms rigidly supported at one end in spaced relation and free to vibrate at their other ends and electromagnetic means for causing said arms to vibrate always in the same direction, said spring arms being selfrestoring and normally held by inherent tension in predetermined position relatively to said actuating means.

31. In an electromagnetic device, the comm bination of a magnetic iield structure, a vibratory armature structure consistlng of a pair of magnetic bars supported at one end on said magnetic structure in substantially parallel spaced relation, and means for connecting said bars near their free ends.

32. In an electromagnetic device, the combination of a magnetic field structure, a vibratory armature structure consisting of a pair of magnetic bars supported at one end on said magnetic structure in substantially parallel spaced relation, the other ends of said bars being free to vibrate in unison, and means whereby said bars always move simultaneously in the same direction.

33. In an electromagnetic device, a magnet having a pair of pole pieces and a pair of vibratory armature bars secured to opposite sides of a pole piece,said armature bars extending on opposite sides of the other pole 80 piece but out of contact therewith to provide two variable airgaps, and means for causing said bars to vibrate always in the same direction.

34. In an electromagnetic device, a. vibratory armature structure consisting of a pair of separate magnetic bars rigidly supportedat one end in substantially parallel spaced re; lation, the other ends of said bars being free to vibrate in unison, and a polarizing coil surrounding each bar.

35. A loud speaker unit having two armatures, a field magnet coacting therewith and means comprising dierential windings for simultaneously increasing the flux densit of one armature while decreasing the flux ensity in the other armature, said windings being stationary and supported independently of said armatures.

ADOLPH A. THOMAS. 

